- Message Transfer
- Message Structure
- Message Delivery
In the battle for supremacy between X.400 and SMTP, SMTP won.X.400 (CCITT and ITU-T)
Comité Consultatif International Téléphonique et Télégraphique (CCITT) was renamed ITU (International Telecommunication Union) Telecommunication Standardization Sector (ITU-T) in 1993. It is based in Geneva, Switzerland. They were the first organization to come up with a set of standards for e-mail called X.400 in 1984 (red book). These were revised in 1988 (blue book).SMTP (IETF)
The Internet Engineering Task Force creates Internet standards in the form of RFCs (request for comments). RFCs are never edited/changed. Instead, they're replaced by new ones. In 1980, RFC 772 specified a mail transfer protocol (MTP), based on the file transfer protocol (FTP). In 1981, RFC 780 improved it, then RFC 788 renamed it to "simple" mail transfer protocol (SMTP). Current standard is RFC 821 (1982).
The destination of an e-mail message can be looked up using DNS based on the domain specified in the e-mail address of the recipient. For example, for email@example.com, a lookup (Windows) of the MX resource record (
nslookup -type=MX adobe.com), brings up this response from Google's DNS:
adobe.com MX preference = 1, mail exchanger = adobe-com.mail.protection.outlook.com adobe.com MX preference = 2, mail exchanger = adobe.mail.protection.outlook.com
RFC 561 defined it for the first time in 1973. Current standard is RFC 822 (1982), along the with the set of MIME standards (RFCs 2045-2049).
In the battle for supremacy here, IMAP4 won over POP3.POP3 IMAP4